In some dry powder inhalers the mouthpiece is partly cleaned from retained drug powder by a wiper that wipes the flat horizontal surface of the mouthpiece insert upon rotation of the mouthpiece. The wiper reduces powder retention in the mouthpiece significantly, verifying that the principle of rinsing with a wiper works. Powder, which may have accumulated on the inner surfaces of the inhaler, is dislodged from those surfaces prior to the next inhalation. In addition, by configuring the inhaler such that the mouthpiece is rotated automatically when the mouthpiece insert holder is removed, it is not necessary to rely upon the user to remember to rotate the mouthpiece prior to each inhalation.
This product improvement has resulted in a correspondingly lower build-up of retained drug powder inside the inhaler, which has significantly lowered the risk of retention losses during use. However, it is clear that further reduction of retained drug powder inside other parts, such as the mouthpiece, of the inhaler is desirable. Improvement of the cleaning function would give a further increased product robustness and reliability.
Mouthpieces for dry powder inhalers use among other means helical devices for breaking up the particulate medicament that is being inhaled by the patient. Cleaning of the channel of the mouthpiece is especially difficult when such helical device is used.
WO 01/95963 discloses a mouthpiece for a particulate inhaler. The known device discloses a mouthpiece provided with a helical member disposed between the inlet and the outlet of the mouthpiece. By air drawn by a user, the helical member undergoes an axial movement between a first and a second position such that it restricts the build up of medicament on the inside of the mouthpiece.
Cleaning in this known device is achieved by axial movement of the helical member in relation to the mouthpiece. The movement of the helical member in the axial direction requires that the length of the mouthpiece is long enough to enable such movement.
In this known device, the axial movement of the helical member is achieved by the force of the air drawn by the user. Cleaning performance thus depends on the flow rate achieved by the patient. The helical member is retained in its initial position by the force of a resilient arm. Thus, the efficiency of the cleaning procedure depends on the user's ability to breath strong enough to overcome the force of the spring and thereby achieve the axial is movement of the helical member. If the device is used by a patient with poor breathing capacity, the cleaning effect might be poor. In that case, medicaments might be built up in the mouthpiece, thus demanding a higher flow rate after each inhalation to achieve a clean mouthpiece. A further risk is that if medicaments continue to be built up on the inside of the inhaler after each inhalation, the helical member might get stuck during the axial movement. Further, for every inhalation a part of the force used by the patient is consumed by the cleaning device, thus leaving less to actually inhale and deagglomerate the dose.